string_decoder 1.3.0: StringDecoder

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify string_decoder.StringDecoder in pkg:npm/string_decoder@1.3.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/string_decoder@1.3.0
Demonstrate these symbols/APIs:
  - string_decoder.StringDecoder
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"case":{"caseId":"case:sha256:711fa9ea160f6c473f0ec31c91348105df4368941621cd1b8201dfee7617da3f","constraints":{"executionContext":"node"},"contract":["StringDecoder instantiates and decodes complete UTF-8 buffers","StringDecoder buffers incomplete multi-byte UTF-8 sequences across chunk boundaries","StringDecoder end with buffer parameter decodes trailing buffer and flushes in a single call","StringDecoder end flushes incomplete trailing multi-byte sequences as unicode replacement character","StringDecoder supports base64, hex, and latin1 encodings","decodeChunks streams and decodes multi-part buffer arrays preserving character boundaries"],"goal":"verify string_decoder.StringDecoder in pkg:npm/string_decoder@1.3.0","kind":"HOW","packages":["pkg:npm/string_decoder@1.3.0"],"schemaVersion":1,"symbols":["string_decoder.StringDecoder"]},"contractCommand":["node","test/contract.js"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"cjs","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/string_decoder@1.3.0"],"schemaVersion":1,"subject":"pkg:npm/string_decoder@1.3.0","symbols":["string_decoder.StringDecoder"],"verifierAdapter":"node-typescript@1"}

const { StringDecoder } = require('string_decoder');

/**
 * Decodes an array of Buffer chunks into a string using StringDecoder.
 * Handles multi-byte characters split across chunk boundaries.
 *
 * @param {Buffer[]} chunks
 * @param {string} [encoding='utf8']
 * @returns {string}
 */
function decodeChunks(chunks, encoding = 'utf8') {
  const decoder = new StringDecoder(encoding);
  let result = '';
  for (const chunk of chunks) {
    result += decoder.write(chunk);
  }
  result += decoder.end();
  return result;
}

/**
 * Creates a configured StringDecoder instance.
 *
 * @param {string} [encoding='utf8']
 * @returns {StringDecoder}
 */
function createDecoder(encoding = 'utf8') {
  return new StringDecoder(encoding);
}

module.exports = {
  StringDecoder,
  decodeChunks,
  createDecoder,
};

{
  "name": "sample-string-decoder",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "sample-string-decoder",
      "version": "1.0.0",
      "license": "MIT-0",
      "dependencies": {
        "string_decoder": "1.3.0"
      }
    },
    "node_modules/safe-buffer": {
      "version": "5.2.1",
      "resolved": "https://registry.npmjs.org/safe-buffer/-/safe-buffer-5.2.1.tgz",
      "integrity": "sha512-rp3So07KcdmmKbGvgaNxQSJr7bGVSVk5S9Eq1F+ppbRo70+YeaDxkw5Dd8NPN+GD6bjnYm2VuPuCXmpuYvmCXQ==",
      "funding": [
        {
          "type": "github",
          "url": "https://github.com/sponsors/feross"
        },
        {
          "type": "patreon",
          "url": "https://www.patreon.com/feross"
        },
        {
          "type": "consulting",
          "url": "https://feross.org/support"
        }
      ],
      "license": "MIT"
    },
    "node_modules/string_decoder": {
      "version": "1.3.0",
      "resolved": "https://registry.npmjs.org/string_decoder/-/string_decoder-1.3.0.tgz",
      "integrity": "sha512-hkRX8U1WjJFd8LsDJ2yQ/wWWxaopEsABU1XfkM8A+j0+85JAGppt16cr1Whg6KIbb4okU6Mql6BOj+uup/wKeA==",
      "license": "MIT",
      "dependencies": {
        "safe-buffer": "~5.2.0"
      }
    }
  }
}

{
  "name": "sample-string-decoder",
  "version": "1.0.0",
  "description": "Verify string_decoder.StringDecoder in pkg:npm/string_decoder@1.3.0",
  "main": "index.js",
  "scripts": {
    "test": "node test/contract.js"
  },
  "dependencies": {
    "string_decoder": "1.3.0"
  },
  "license": "MIT-0"
}

{
  "schemaVersion": 1,
  "goal": "verify string_decoder.StringDecoder in pkg:npm/string_decoder@1.3.0",
  "kind": "HOW",
  "packages": [
    "pkg:npm/string_decoder@1.3.0"
  ],
  "symbols": [
    "string_decoder.StringDecoder"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

const assert = require('node:assert');
const { StringDecoder, decodeChunks, createDecoder } = require('../index.js');

// 1. Instantiation and basic decoding
{
  const decoder = createDecoder('utf8');
  assert(decoder instanceof StringDecoder);
  const result = decoder.write(Buffer.from('Hello, CodeSampleX!'));
  assert.strictEqual(result, 'Hello, CodeSampleX!');
  assert.strictEqual(decoder.end(), '');
}

// 2. Decode multi-byte UTF-8 sequence split across chunks (2-byte character: 'é' -> 0xc3 0xa9)
{
  const decoder = new StringDecoder('utf8');
  assert.strictEqual(decoder.write(Buffer.from([0xc3])), '');
  assert.strictEqual(decoder.write(Buffer.from([0xa9])), 'é');
  assert.strictEqual(decoder.end(), '');
}

// 3. Decode multi-byte UTF-8 sequence split across chunks (3-byte character: '한' -> 0xed 0x95 0x9c)
{
  const decoder = new StringDecoder('utf8');
  assert.strictEqual(decoder.write(Buffer.from([0xed, 0x95])), '');
  assert.strictEqual(decoder.write(Buffer.from([0x9c])), '한');
  assert.strictEqual(decoder.end(), '');
}

// 4. Decode 4-byte UTF-8 emoji split across multiple chunks ('🚀' -> 0xf0 0x9f 0x9a 0x80)
{
  const decoder = new StringDecoder('utf8');
  assert.strictEqual(decoder.write(Buffer.from([0xf0])), '');
  assert.strictEqual(decoder.write(Buffer.from([0x9f, 0x9a])), '');
  assert.strictEqual(decoder.write(Buffer.from([0x80])), '🚀');
  assert.strictEqual(decoder.end(), '');
}

// 5. end(buffer) decodes the trailing buffer and flushes
{
  const decoder = new StringDecoder('utf8');
  assert.strictEqual(decoder.write(Buffer.from([0xf0, 0x9f])), '');
  const endResult = decoder.end(Buffer.from([0x9a, 0x80]));
  assert.strictEqual(endResult, '🚀');
}

// 6. Incomplete trailing multi-byte sequence flushes replacement character on end()
{
  const decoder = new StringDecoder('utf8');
  assert.strictEqual(decoder.write(Buffer.from([0xed, 0x95])), '');
  assert.strictEqual(decoder.end(), '\ufffd');
}

// 7. Supports different encodings: base64, hex, latin1
{
  const b64Decoder = new StringDecoder('base64');
  assert.strictEqual(b64Decoder.write(Buffer.from('Hello ')), 'SGVsbG8g');
  assert.strictEqual(b64Decoder.end(Buffer.from('world')), 'd29ybGQ=');

  const hexDecoder = new StringDecoder('hex');
  assert.strictEqual(hexDecoder.write(Buffer.from([0xab, 0xcd])), 'abcd');
  assert.strictEqual(hexDecoder.end(Buffer.from([0xef])), 'ef');

  const latin1Decoder = new StringDecoder('latin1');
  assert.strictEqual(latin1Decoder.write(Buffer.from([0xe9, 0xf1])), 'éñ');
  assert.strictEqual(latin1Decoder.end(), '');
}

// 8. decodeChunks helper function streams chunks correctly
{
  const chunks = [
    Buffer.from([0xed, 0x95]),
    Buffer.from([0x9c, 0x20]),
    Buffer.from([0xf0, 0x9f]),
    Buffer.from([0x9a, 0x80]),
  ];
  assert.strictEqual(decodeChunks(chunks, 'utf8'), '한 🚀');
}

console.log('All StringDecoder contract assertions passed.');